They gave six rats an overdose of anaesthetic and found that serotonin levels in their brains had tripled by the time they died (Neuroscience Letters, DOI: 10.1016/j.neulet.2011.04.051).

Wutzler expects to see a similar increase in dying human brains. He says serotonin could be behind NDEs, but Jakob Hohwy at Monash University in Melbourne is unsure. "One thing that you don't want to say is that rats have NDEs," he says.

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